1. Field of the Invention
This invention relates to a process for converting (1) an indene, (2) a polyindene, (3) a dihydronaphthalene or (4) a polydihydronaphthalene to 4-nitro-o-phthalic acid which comprises nitrating said indene, polyindene, dihydronaphthalene or polydihydronaphthalene and then oxidizing said nitrated indene, polyindene, dihydronaphthalene or polydihydronaphthalene with nitric acid.
2. Description of Prior Art
A logical procedure for preparing 4-nitro-o-phthalic acid would appear to involve the nitration of phthalimide to give 4-nitrophthalimide and hydrolyzing the latter. The synthesis is costly, however, because of the low yields of 4-nitro-o-phthalic acid obtained (50 to 52 per cent) and the cost of the phthalimide [Organic Synthesis, Col. Volume II, John Wiley and Sons, New York, 1943, pages 457 to 459].
If, on the other hand, phthalic acid or phthalic anhydride is nitrated, an approximately 50/50 mixture of 4-nitro-o-phthalic and 3-nitro-o-phthalic acids is obtained. This reaction is a known procedure for the synthesis of 3-nitro-o-phthalic acid, despite the low yields (28 to 31 per cent) of 3-nitro-o-phthalic acid obtained. [Organic Syntheses, Col. Volume I, John Wiley and Sons, New York, 1932, pages 408 to 412]. In preparing 3-nitro-o-phthalic acid by this method, advantage is taken of the lower water solubility of 3-nitro-o-phthalic acid. The latter material is then recovered by crystallization from water. 4-Nitro-o-phthalic acid can be obtained from washings and other liquors after separation of 3-nitro-o-phthalic acid via evaportion, esterification, separation of isomeric esters and subsequent hydrolysis of the separated ester of 4-nitro-o-phthalic acid. This procedure would be expected to be laborious, costly and to result in low yields of 4-nitro-o-phthalic acid.